Positronium formation in sol–gel-prepared silica-based glasses: temperature and positron-irradiation effect

Positron annihilation and free volume studies in polymer glasses

“…For the compounds mentioned above, in the number of previous publications, a complex, bimodal character of lifetime distribution of o-Ps decay was described. 17,19 The same property was fixed for inorganic glassy materials, such as sol-gel-prepared silica-based glasses 21 and low-k dielectric thin glassy films produced by introduction of some amounts of porogen (later thermally decomposed) into methyl-silsesquioxane (MSSQ). 22 ORTHO-POSITRONIUM ANNIHILATION LIFETIME SPECTRA Elastic and glassy polymers are normally considered as homogeneous disordered materials with a unimodal (symmetric, Gaussian, for example) distribution of elementary free volumes.…”

Effect of hydrogen bonding on low temperature positronium formation in frozen hexanol

“…These positrons can also migrate away from the terminal spur and interact with free electrons or trapped electrons in the shallow potential created among polymer chains. The Ps formation probability in polymers is influenced by many factors, affecting injected positrons and excited electrons: chemical composition and electronic structures of molecules, electric fields [1], motion and mobility of polymer structures [3], crystallinity [4] and temperature [5][6][7][8].…”

Some Aspects of Free Volume Studies in Molecular Substances Using Positron Annihilation Experiments

“…2 in Ref. [15]), though predicting a decrease in the longest lived o-Ps lifetime on heating, does not give a good enough fitting to the experimental points over the entire temperature range between 50 and 350 K. The slope of experimental dependence is too flat compared to the theory. For example (LPS200X, Fig.…”

“…Alternative approaches to the problem are illustrated on example of polyimides (temperature dependence experiments [4][5][6][7][8][9]) and on example of low-density cross-linked polymeric sorbents [10][11][12][13][14][15][16][17] (Table), TABLE PATFIT and MELT results for the lifetime spectra (first and second lines for RT and LT, correspondingly) of polymeric sorbents described in [11][12][13]. Letters ρ and S with subscripts are used to denote density (in g/cm 3 ) and specific surface of the samples (in m 2 /g) measured in two different ways [11].…”

“…3), if the model curve is normalized on high-temperature data, an increase in experimentallifetime at low temperature is not as strong as it is expected from the theory. For silica-based glasses and polystyrenes, an explanation of this discrepancy was found [10,11,15] in combination of the "large hall" effect with chemical interaction of positronium with radicals induced by irradiation and stored in a sample during the experiment with positron source at low temperature or with atmospheric oxygen strongly trapped between aromatic rings. However, another discrepancy comes out when the estimations of the pore size found on the bases of the ETE model and sorption experiments are compared.…”